So the nucleus is certainly the brains, the operation of the cell.
So the nucleus is a spherical structure.
It's bound in a double membrane. And it has nuclear pores.
It actually got pores all over it so that things
can move in and out of the cell.
And we used to think things move pretty freely
into and out of the cell.
However it turns out that the nucleus is
pretty selective about what it lets in and out
as the cell membrane is fairly selective
about what it lets in and out.
Inside the nucleus, again we have the DNA,
generally it is unwound in its chromatin form
because the cell needs to access the DNA in order to
produce proteins through transcription and translation
in order to make proteins that support the cell's functions.
Must take a little bit closer look at
the nuclear pores that we see in the cells.
Again, the nucleus is a double phospholipid bilayer.
So two phospholipid bilayers with a little bit of space in between.
There is a protein pore going through the cell
as we've looked at in previous lectures.
These proteins, this is one of where the protein has function
allows a channel for things to move through.
Recently we've learned that that protein pore has
a little bit more detail in selectivity.
We know that on the internal surface we have this nuclear basket
and that basket is going to control how things
move in and out through the pore
It's not quite clear yet how it does this,
but we do know that it's involved in this.
And on the outside of the nucleus, on the outer membrane,
we see that there are some fibers that perhaps
even sweep things in towards that nuclear pore.
So these pores are much more selective
than we had previously thought.
So now, we understand these nuclear pores and
that we have a nucleoid region inside of the nucleus
where we'll see that much of the RNAs produced to compose ribosomes.
I think it's time for us to take a look at the ribosome itself.
Ribosomes can either be free floating around in the cell
or they can be bound to the endoplasmic reticulum.
Ribosomes are the protein making factories of the cells.
They are composed of two subunits.
Again, the subunits are built primarily of
RNA and a little bit of protein.
And they're often assembled in the nucleoid region of the nucleus.
So we have a large subunit, and we have a small subunit.
And they stay apart actually until it's time for them to take
a DNA message on messenger RNA and actually manufacture a protein.
So large subunit and small subunit could be
floating around in the cytoplasm.
And if it's time to make a protein,
if there's messenger RNA floating around,
then they'll assemble on that messenger RNA
and start translating that code into a protein
in order to either make the protein to stay or to go.